Advances in technology have resulted in smaller and more powerful computing devices. For example, there currently exist a variety of portable computing devices, including wireless computing devices such as wireless telephones, personal digital assistants (PDAs), and tablet computers that are small, lightweight, and easily carried by users. In order to simplify user interfaces and to avoid pushbuttons and complex menu systems, such portable computing devices may use touch screen displays that detect user gestures on the touch screen and translate the detected gestures into commands to be performed by the device. Such gestures may be performed using one or more fingers or a stylus type pointing implements in contact with or in close proximity to a sensing surface. The term Quality-of-Service (QoS) is collectively used to represent several properties of touch screen implementations such as position update rate, accuracy of determined touch position, touch position determination resolution, the maximum number of objects tracked simultaneously, the cross-sectional size of tracked objects, usage modalities such as contact or contact-less operation, detection sensitivity, etc.
Due to the coarse cross-section of an average human finger, finger-based touch input can be used for operating coarse controls on the user interface, such as selecting an item or pressing a button. Such finger-based use cases require only low Quality of Service (QoS). Use cases such as on-screen drawing, calligraphy, or handwriting capture for example, require a fine-tipped input tool or stylus to allow the touch sensitive surface to capture finer movements. Such stylus-based use cases require a much higher QoS. Existing touch processing implementations intended to support applications requiring high QoS are statically configured to operate continuously at a high QoS even when the current application does not support stylus input. Since higher QoS translates to high energy consumption, such static implementations are not energy efficient. Due to the latest trend in mobile computing and communication devices having large display sizes, varied applications boast different modes (finger, stylus, and proximity) of touch-based human interfaces and use-cases. The resulting complexity of the touch sensing implementation means that touch processing is increasingly threatening battery life while delivering sub-optimal user experience most of the time.